Grinding machine with crush



L. F. PoLK Re. 23,739

GRINDING MACHINE WITH CRUSH-DRESSING ATTACK-WENT Nov. 17, 1953 2Sheets-Sheet l Original Filed June 4, 1945 Nov. 17, 1953 1 F. PoLK Re.23,739

GRINDING MACHINE WITH CRUSH-DRESSING ATTACHMENT Original Filed .June 4,1945 2Sheets-Sheet 2 u fa mi l mzlve mm ffm-m k BY 'zdrmm man?. M :z w

. 1 v ATTORNEY Reissued Nov. 17, 1953 UNITED STATES PATENT OFFICEGRINDING MACHINE WITH CRUSH- DRESSING ATTACHMENT Louis F, Polk, Dayton,Ohio, assignor to The Sheffield Corporation, Dayton, Ohio, a corporationof Ohio Original N0. 2,477,418, dated July 26, 1949, Serial No. 599,237,June 4, 1945.

Application for reissue December 23, 1952, Serial No. 327,709

14 Claims.

Matter enclosed in heavy brackets reissue specification;

'I'his invention relates to grinding machines and more particularly tomeans for forming or surfacing the grinding Wheel of such a machine, theinvention being applicable to form grinders or surface grinders or thelike.

One object of the invention is the provision, in a grinding machine, ofa grinding wheel truing device including a plurality of rotatablecrushers adapted for operation on the grinding wheel, one of thecrushers shaping the grinding wheel to approximately the desired shape,while the second crusher gives the final or accurate form as desired.

Another object of the invention is the provision, in a grinding machine,of a grinding wheel truing device, having a pair of crusher wheelscarried for simultaneous movement by holding mechanism whereby thecrushers can be moved in one direction to bring one of them intopressure engagement with the grinding wheel, and then be moved in asecond direction so that the first crusher is released from the grindingwheel and the second crusher is brought into pressure engagement withthe wheel.

Another object is the provision of a-grinding wheel truing device havinga movable slide mechanism on which a pair of crushers are arranged, thecrushers being so moved that one of them may be brought into engagementwith the grinding wheel and produce a crushing operation on the wheelfor a desired time interval, and at the end of that interval, thecrushers are automatically moved in a direction at an angle to thedirection in which they rst moved, to bring the second crusherintopressure engagement with the wheel.

Another object of the invention is the provision, in a grinding machine,of a grinding wheel tracing device including means for relatively movinga grinding wheel and a crusher means toward one another in a series ofautomatically coordinated sequential movements in directionssubstantially transverse of one another.

Another object is the provision of a crusher mechanism for a surfacegrinder or the like, in which a crusher supporting slide is slidablyarranged on a crusher supporting base and is yielding on that base whenthe base is moved to bring a crusher into an engagement with thegrinding wheel, the construction being such that after a predeterminedyielding movement of the crusher slide, a solenoid lock is automaticallyenergized to hold the crusher slide on the base and a further controlledmovement of the crusher slide then takes place throughout a timeinterval determined by .a suitable timing mechanism.

appears in the original patent but forms no part of this matter printedin italics indicates the additions made by reissue.

`surface grinders, or the like;

Fig. 2 is a side elevation, partly in section, showing the relationshipbetween the grinding wheel and the crusher adjusting mechanism;

Fig. 3 is a top plan view of the crusher adjusting mechanism;

Fig. 4 is a vertical section on the line 4--4 of Fig. 3;

Fig. 5 is a vertical section on line 5 5 of Fig. 2;

Fig. 6 is a wiring diagram;

Fig. '7 is a timing chart showing the sequential operations that takeplace; and

Fig. 8 is a diagrammatic showing of how the grinding wheel is drivenfrom the power drive motor or from the auxiliary slow speed drive motor.

Referring more particularly to the drawing, in which the same referencenumerals are used to designate like parts in the different views, 20generally represents the frame structure of a grinding machine having arotatable grinding wheel 2|. The grinding machine may be of the typehaving a movable table 23 that reciprocates back and forth and carriesthe work past the grinding wheel, or it may be of the character moreparticularly used in grinding threads or forms on workpieces heldbetween centers. Any suitable mechanism such as a reversible motor 3Acan be used to move the work supporting table 23 back and forth belowthe grinding wheel, and carry the work arranged in a suitable holder 24.At the end of the grinding operation, or any other time it might bedesired to true the surface of the grinding wheel, the table 23 is movedto the left beyond its normal travel stroke and brought up to apredetermined position in which the grinding wheel is spaced only alittle distance from the truing crusher.

In accordance with the present invention, a plurality of rotatablecrushers are employed to form or true the grinding wheel to its intendedshape. One of these crushers gives a preliminary truing action as thegrinding wheel and the crusher are rotated in pressure engagement withone another at suitably slow speed. The rst crushing operation gives anapproximation to the required shape, the exact shape of the grindingwheel desired being produced by the second crushing operation under theaction of the second crusher while the grinding wheel and cspso f. 1i 'j3 its crusher are rotated in pressure engagement with one another. Thetwo .crushers can have approximately the same form and shape, vifdesired, and as wear takes place on the first crusher because of its usethrough longer time periods,

any change in its shape will be relatively uni-m portant, since thesecond crusher will give the exact shape desired and will maintain itsform over long periods of tima-not vbeing called upon to perform themajor portion of the crushing operation. If desired, a portion of theformations or curves may be gfiyen to the Agrinding wheel by the rstcrusherand other portions of the grinding wheel subsequently formed bythe second crusher. In either case, the two .Crushers act to complementone another in producing the lexact Vshape desired on the grinding wheelperiphery.

As shown in Fig. 2, the crusher that first acts on the :grinding Wheelsshown at. .25. anathesecondcrusheris illustrated at 21. These .twocrushers are rotatably supportedfor free movement on arbors carried' bythe holder 28, which is slidably carried for vertical movement on acrusher table slide This slide operates horizontally on the Crusherbase3ll which iS fixed on theworlicarrying table .2.3 of the machine.Normally, at thevstart of a. cycle .of operation, the holder 2.8 is in a.lowered position so that the axis -of th-e .crusher 2S is horizontally`arranged from the axis of the grinding wheel 2|, with the .Crusherslightlyspaced for the grinding wheel. This is'the position at which thetable 23 is stopped and held at the end of-a normal grinding operationon the work. Movements of the V.Crusher then ,take place. horizontallyand'vertically by means .O the virlechanisrn that will now be described.

The holder 2.8 is vertically adjustable along the slide 2,9 by means ofa rack 32 on the holder and a spur gear 33 which is rotatably arrangedona ,shaft 34 carried .by the crusher ,slide 29. .The gear .33r carries aclutch face ,3 5 Aso it mayv be coupled to a rotatable clutch collar 3.6which is keyed to the shaft The shaft is driven by ,an electric motor.5A von ,the slide. The clutch Ycollar .3e is Vautomatically controlledby ayoke 3B moved by .an arm 3s pivoted at 40 yand operated in onedirection-or the otherby solenoids 1A and B A as shown in Fig. dI-Byclosing] When the solenoid VEAL] ,is closed the shaft .3.4 will becoupled -to the gear 33 and the holder 2,8 will be raised. When thesolenoid "IA isenergized, the shaft 34 is coupled to clutch ldisc 4Iwhich is fixed on a kgear 2. meshing with gear 44 .on a yerticalshaitQ5. .On the lower end rof this shaft is a worm .4 6 turning a worm wheel41. This worm wheel is threadedon a non-rotatablefeed shaft to ,spline'dinthe slide-29, the worm Wheel being held against axial rum/.ement withrespect tothe [orusher base] i235] slide 2.9.v In this way, theAoperation .of the motor 6A can drive the feed nut 5i) on shaft 23 at aregular predetermined slow speed and cause a predetermined feed movementof the crusher slide toward the grinding wheel. This slide movementtakes place if A the feed shaft e3 is held against axial movement withrespect to the base 30, and the shaft is so held, at times, .by means ofan electric securing meanssuch as .a magneticllock 4A, which holds vrtheshaft s securely to the base 3U. When this v magnetic lock is notenergized; relative movement of the Crusher slide 2s toward the right asviewed -inFig 2 isrestrained only by a spring 52A interg posedv betweenvthe end of the slide Z3 and [a4 flange on shaft 48 contacting] themagnetic lock. It will be understood that as thejwork supporting table23-is moved to the left as viewed in Fig. 2, the crusher 2E in itslowered position will engage the grinding wheel, and as this left-handmovement of f the table continues, the spring 52 Iwillzbe compressed,slide 29 being forced to the right with respect to the Crusher base 3H.Alf-ter a predetermined relative motion has taken place in this way, aswitch arm 54 of a limit switch B `carried by the crusher slide 29 willride up an abutment 5 5 on the base 35 and control this limit switch,the effect of which will be presently described. There is another limitswitch carried by the Crusher table slide 29 in such position as to beoperated by the holder 28 when the holderhas been raised toapredetermined position inY the ICrusher El is horizontally opposite thegrinding wheel 2l.

During the normal grinding operation, the grinding wheel 2 I is rotatedat comparatively high speed by a power drive motor IA `a portion ofwhich is shown in .F ig.' 1, the motor being also diagrammaticallyillustrated vin Fig. 6, where it is shown connectedthrough theswitch lawhich is closed when the relay I is closed. The relay I is arranged incircuit with a normally closed switch 2a connected through a stop.switch 58'and start switch 5B to the secondary 60 of a transformer thatis `supplied with current from a suitable power source 62. The switch 59is momentarily closed in carrying outA a normal grinding operation [but],and a switch 1b actuated by relay 1 maintains a y circuitv around it.The circuit through the relay 1 should be open during the crushingoperation. For crushing, a switch 63 is closed and thisconnects 4througha stop switch 64 and through anormally closed limit switch Sto a relay2. SwitchASis carried by the frame 20 and is temporarily opened by a lugon the table 23 as will vbe later described. The relay 2, whenenergized, opens switch 2a t0 make sure the power drive motor IA willnot operate. Relay 2 also closes [two] switches 2b, [and] 2c[, one ofwhich] and 2d. ,Switch 2b is a holding switch around the start switch 63[and the otherl Switch 2c connects one side of the supply line to aseries of cam operated switches and relay coils 3 to I 0 inclusiveaud'switch Zd completes a circuit around the cam operated switchassociated with 'relay Y10 for purposes vlater described. Switch 2calso` connects an automatic timer motor 6E, through the limit switch B.The relay coils 3 to I0 each are in series with switches controlled bycams operated by the timing motor EB so as to give the desired sequenceof operation. as illustrated inthe timing diagram shown in Fig. 7.

The relay coil 8` is in series with the limit switch E which iscontrolled by the vertical movement of holder 28 as previouslymentioned. Relay 8 is eiective, when it is energized, to open thenormally closed switch 8a in series with relay 9. A switch 3a operatedby relay 3 supplies power to the reversible electric motor 3A whichtraverses the worktable 23, Switch Illa, controlled by relay Hl,supplies power for the reverse operation of this motor. Switch 4acontrolled by relay 4 enerv gizes the crusher table slide lock 4A.Switch 5a closes when relay 5 ,is energized and supplies power to`anauxiliary drive motor 5A, which operates throughfa clutch 10 to turnthe grinding wheel 2| at comparatively slow speedy duri-ng the crushingVoperation, the main power motor IA being de-energized underY theseconditions. The clutch 1.0 isanover-rzunning clutch offany. ksuit- Wheelwill be turned at a peripheral speed of about 300- feet a minute,suitable for a crushing operation. Switch 9a when energized by relay 9energizes the crusher holder lock 9A which is supported on a bracket 68on the crusher table slide 29. When this is energized it electricallylocks the rod 69 which is fixed on the holder 28 so as to secure theholder firmly to the slide 29.

The sequence of operations in automatically crushing the grinding wheelfirst with the preliminary crusher 26 and then with the finishingcrusher 21 is as follows:

After a predetermined number of passes across the work, the table 23moves over to a predetermined work loading position so that the grindingwheel is adjacent to the crushers. When a crushing operation is desired,it is initiated from this position by closing the switch 63, the switchS being closed and untripped, the vfollowing operation taking place:

Relay 2 is energized, opening switch 2a so as to block out the normalgrinding motor IA. At

the same time holding switch 2b is closed around the starting switch 63,[and] the normally open switch 2c is closed in series with the relay 3and switch 2d is closed. Energizing relay 3 closes switch 3a and startsthe traverse motor 3A for the table 23 so the crusher is moved overtowards the grinding wheel.

As the crusher contacts the grinding wheel a differential movement ofthe crusher table slide l 29 and the crusher base 30 takes place, spring52 being compressed. This movement first closes the limit switch B whichsets the automatic timer motor 66 in operation. When the timer isstarted, the traverse of table 23 is de-energized by opening the relay 3through its cam operated control switch. The crusher table lock 4A isenergized locking the shaft 4B to the crusher base. The crusher holderlock 9A is also energized, holding the crusher roll 26 horizontallyopposite the vgrinding wheel. The timing motor 66 then closes the relays5 and E, thus energizing the auxiliary drive motor 5A for the grindingwheel and energizing the crusher adjusting motor 6A. At the same time,the shifting solenoid 1A is energized to Shift the clutch coZZafr 36 tocouple shaft 34 to the clutch disc 41 so as to drive shaft 45 and [toengage the clutch collar with the shaft 45 so as to] turn the worm wheel41. This initiates a slow positive feed of the crusher in a horizontalfeed. Any desired means can be used to mooe the clutch disc to anintermediate position, for example, as illustrated the contour of theteeth on the clutch faces is such as to cam the disc to a neutralposition when the solenoids are de-energized. After suflicient time haselapsed for the grinding wheel to make about two revolutions with thecrusher feed stopped, the relay 5 is deenergized by its cam operatedswitch, stopping the auxiliary grinding wheel drive motor 5A. Afterenough time has then elapsed for the grinding wheel to stop rotating,the locking solenoid 4A is de-energized, the holder locking solenoid 9Ais de-energized and the shifting solenoid 8A is energized. This movesthe clutch disc so that the crusher holder 26 will be raised thusbringing the crusher roll 21 into contact with the grinding wheel. Thisis the position of the p-art shown in Fig. 2. As crusher 21 engages thegrinding wheel, the spring 52, which expanded as crusher 26 moved away,will be contracted again as the effective diameters of the two Crushersis approximately the same.

When the crusher 21 reaches a position in horizontal alignment with thegrinding wheel, the limit switch E is opened, rie-energizing relay 8 andopening the switch 8a breaking the [holding] circuit of the shiftingsolenoid 8A. At the same time the shifting solenoid 1A is energized,thus [energizing] moving the clutch disc to couple the shaft 34 to thefeed screw nut 41. This causes a positive feed of the crusher roll intothe grinding wheel, since the magnetic locking solenoid 4A is closedagain by the cam switch. 'I'he cam switch for the slide locking solenoid9A on the automatic timer is also closed during the time the crusherholder is being raised but cannot energize the slide locking solenoid 9Abecause of the open electricV switch 9a opened by the energized relay 8.Therefore, when the limit switch E is opened, breaking the circuitthrough the relay 8, the switch 6a is closed, completing the circuitthrough relay 9 and causing the simultaneous energization of solenoid 9Awhile the shifting solenoid 8A is de-energized. At the same time, theauxiliary drive motor 5A for the grinding wheel is energized and thegrinding wheel starts to rotate slowly.

After a predetermined amount of feed of the crusher slide by the crusheradjusting motor 6A energized through the closed relay E, the motor 6A isautomatically de-energized by the automatic timer which opens thecircuit through the relay 6. At the same time the shifting solenoid 1Ais de-energized to [disengage] release the clutch disc and [shift it]allowes its movement to a neutral position.

After enough time has taken place for the grinding wheel to make abouttwo or three revolutions with the crusher feed inoperative, the grindinglwheel auxiliary drive motor 5A is de-energized b-y -de-energizing therelay 5. Then after enough time has elapsed for the grinding wheel tocome to a complete stop, the table traverse motor 3A is started by theautomatic timer closing the circuit through the relay I0 closing switchIlla, and the table then moves from the grinding wheel to retract thecrushers horizontally to the loading position of the table 23.

While the table of the grinder is being moved to the right, as justmentioned, the slide locking solenoid and the holder locking solenoid 4Aand 9A are de-energized an-d the automatic timer completes its cycle ofoperations and interrupts its own circuit. When locking solenoid 9Adeenergizes, the holder descends by the force of gravity until it isstopped in lowered -positionwith crusher 26 opposite the grinding--Wl'leel.v Even though ther timer-has. completed its operation and. .thecam switch .forxthe table traverse controlling relay @ID `has beenopened, a lcircuit is completed through the relay I around its cam.operated switch throughl switch 2d until the table 23 reaches itsoriginal position, when the relay 2 is dez-energized [holding circuit 2aisv interrupted] bythe tripping of the limit switch S operated bythetable 23,thus completing-the crushing cycle.

While the form of apparatus herein described constitutes a preferredembodiment of the invention in a form applicable-to a grinding machinesuch as-a surface grinder, it is to be understood that theinvention isnot limited to this precise form of apparatus, and that changes may bemade therein without Vdeparting fro-m the scope of the .invention whichis` denedin the appended claims.

vWhat is claimed is: l. A grinding machine having a frame and a grindingwheel rotatably mounted thereon, a pair of rotatable crusherssequentially operable on the grinding wheel to true the surface of thewheel,

'aicom-mon holder [for] carrying said Crushers, a

slide on which said holder is mounted, a slide confnection between saidholder and slide and a slide vconnection between said slide and frame,means including one of said slide connections for moving said holder toadjust one of the Crushers relatively to the grinding lwheel forcrushing the grinding wheel to the approximate form desired, and meansincluding the other of said slide connections for moving the crusherholder rectilinearly in a plane transverse of the grinding wheel .axisto bring the second crusher into operative engagement with the grinding`wheel to inish the 'trueing operation.

2. A grinding machine having a frame and a grinding wheel rotatablyAmounted thereon, a pairof rotatable Crushers, a holder [for] carryingsaid Crushers, means supporting said holder for rectilinear-movementtowards the grinding wheel, means supporting said holder for rectilinearmovement'in a direction substantially transverse to the iirst direction,said two means comprising a slide on the frame slidably supporting `saidholder, means providing for yielding movement of theholder with respectto the grinding Wheel and means for operating said holder on vsaid slideto disengage one of the Crushers and cause the engagement of the secondcrusher with the grinding wheel.

i3. A grinding machine having a frame and a grinding wheel rotatablymounted thereon, a

' crusher holder, rotatable crushing means on said holder for trueingthe surface of the grinding wheeL means supporting said holder on saidframe for movement in a plurality of directions substantially transverseof one another, and

' power operated means operatively connected to saidholder for movingsaid holder sequentially rst in one direction at a controlled rate tocause approach of the axes of the grinding Wheel and the crushing means,and then in a second di- `supporting said holder for ,rnovementin one fdirection ina plane-.transverse of the grinding @wheel axis,- .lmeanssldeably supporting said .slide 28 :means Y fors-movement a; seconddirectienin: a planetransverse of the.V grinding Wheel axis and at asubstantial angletosaid rstdi-rectiom-an adjusting-motor carriedbyfnoneof said-means. drive mechanism -operably connected to vsaid motorfor adjusting theslide-means-and adjusting the -holder on the slidemeans to vary the distancebetween the axes of the crusherswith respectto the grinding wheel axis, and clutch means controlling saiddrivemechanism.

5. A grinding machine-having a frame anda grinding wheel .rotatablyymounted thereon, -a roughing crusherY operable tofform the surface ofthe grinding Wheel to the approximate yshape desired, a finishingcrusher'for accurately finishing -the wheel after they roughingVcrusherY has been applied to the wheelra common holder on which saidCrushers are rotatablyv mounted, means providing for yielding movementof said holder with respect to thegrinding wheel, and means comprisingmechanical adjusting devices andY electrical control switches operablein conjunction-'therewith for controlling said holder` to sequentiallymove the roughingcrusher into yielding pressure engagement with ithewheel, then positively move the roughing crusherrtowards the grindingAwheel axis, then move t-he finishing crusherinto yielding pressureengagement with the wheel and then positively move the iinishing crushertowards the grinding wheel axis.

6. A crusher mechanism adapted to be usedto form a grinding wheelcomp-rising a pairv of rotatable crusher-s, a holder [for] carrying-saidCrushers and slide lmeans slidably supporting said holder for movementin a plane transverse of kthe crusher-axes in onedirection generallytowards the grinding Wheel axis and in a second direction substantiallytransverse of said one direction, an adjusting motor carried by -sa'idslide means, drive mechanism operably `connected to said motor foradjusting the slide means and the holderl on the slide means, andclutchmeans controlling said drive mechanism tov sef quentially move one ofthe Crushers into crushing engagement with the grinding wheel and thenmove said crusher out of engagement with the grinding Wheel'and bringthe other crusher into crushing engagement with the grinding wheel.

7. A crusher mechanism adaptedv to be used to form agrinding Wheelcomprising-a pair of rotatable Crushers, a holder for said Crushers andslide means slidably supporting said holder for movement in a planetransverse ofthe crusher axes in one direction, generally towards thegrinding wheel axis and in a second direction substantially transverseof said one direction, an adjusting motor carried by said slide means,drive mechanism operably connected to said motor for adjusting the slidemeans and the holder on the slide means,` means for. yieldingly...substantially transverse of one another, and power operated meansyoperatively connected to said holder for .moving-v said holdersequentially Jirst in one direction-at a controlled rateto causeapproachvof the axes of the grinding wheel and the crushing means, andthen in a second direction substantially transverse of said onedirection to gradually change the distance between thepaxes of thegrinding wheel and the crushing means, and control means operativelyassociated with said power'operated means and said holder toautomatically initiate the movement in the second direction followingcompletion of the holder movement in the first direction. l

' 9. A grinding machine having a frame and a grinding wheel rotatablymounted thereon, a crusher holder, rotatable crushing means on saidholder for truing the surface of the grinding wheel, slide meanssupporting said holder on said frame for rectilinear movement in aplurality of directions substantially transverse of one another, poweroperated means operatively connected to said holder for moving saidholder sequentially first in one direction at a controlled rate to causeapproach of the axes of the grinding wheel and the crushing means, andthen in a second direction substantially transverse of said onedirection to gradually change the distance between the ames of thegrinding wheel and the crushing means, and control means operativelyassociated with said power operated means and said holder toautomatically initiate the movement in the second direction followingcompletion of the holder movement in the first direction.

10. A grinding machine having a frame and a grinding wheel rotatablymounted thereon, a work supporting table, means supporting said table insaid frame for reciprocatory movement past said grinding wheel, acrusher holder, rotatable crushing means on said holder for truing thesurface of the grinding wheel, means supporting said holder on saidtable for movement relative thereto in a plurality of directionssubstantially transverse of one another, and means for moving saidholder relative to said table sequentially first in one direction at acontrolled rate to cause approach of the aes of the grinding wheel andthe crushing means, and then in a second direction substantiallytransverse of said one direction to gradually change the distancebetween the ames of the grinding wheel and the crushing means.

11. A grinding machine having a frame and a grinding wheel rotatablymounted thereon, a work supporting table, means supporting said table insaid frame for reciprocatory movement past said grinding wheel, acrusher holder, rotatable crushing means on said holder for truing thesurface of the grinding wheel, means supporting said holder on saidtable for movement relative thereto in a plurality of directionssubstantially transverse of one another, power operated meansoperatively connected to said holder for ymoving said holder relative tosaid table sequentially first in one direction at a controlled rate tocause approach of the ames of the grinding wheel and the crushing means,and then in a second direction substantially transverse of said onedirection to gradually change the distance between the ames of thegrinding wheel and the crushing means, and control means operativelyassociated with said power operated means and said holder toautomatically initiate the movement in the second direction followingcompletion of the holder movement in the first direction.

12. A grinding machine having a frame and a grinding wheel rotatablymounted thereon, means for rotating said grinding wheel at grindingspeed, a work supporting table, means supporting said tablein'said framefor reciprocatory movement past said grinding wheel, a crusher holder,rotatable crushing means on said holder for truing the surface of thegrinding wheel, means supporting said holder on said table for movementrelative thereto in a plurality of directions substantially transverseof one another, power operated means operatively connected to saidholder for moving said holder relative to said table sequentially firstin one direction at a controlled rate to cause approach of the ames ofthe grinding wheel and the crushing means, and then in a seconddirection substantially transverse of said one direction to graduallychange the distance between the axes of the grinding wheel and thecrushing means, control means operatively associated with said poweroperated means and said holder to automatically initiate the movement inthe second direction following completion of the holder movement in thefirst direction, drive means for relatively rotating said grinding wheeland said crushing means at a comparatively slow crushing speed, andmeans connected to said drive means and operatively associated with saidholder to automatically energize said drive means following apredetermined holder movement in the first direction.

13. A grinding machine having a frame and a grinding wheel rotatablymounted thereon, a crusher holder, rotatable crushing means on saidholder for truing the surface of the grinding wheel, slide meanssupporting said holder on said frame for rectilinear movement in aplurality of directions substantially transverse of one another, power:operated means operatively connected to said holder for moving saidholder sequentially first in one direction at a controlled raie to causeapproach of the apes of the grinding wheel and the crushing means, meanscooperating with said crusher holder providing for yieldable contact ofthe grinding wheel and the crushing means upon the holder movement inthe first direction, said power operated means including means for thenpositively moving the crusher holder in a second direction substantiallytransverse of said one direction to gradually change the distancebetween the ames of the grinding wheel and the crushing means, andcontrol means operatively associated with said power operated means andsaid holder to automatical'ly initiate the movement in the seconddirection following completion of the holder movement in the firstdirection.

14. A grinding machine having a frame and a grinding wheel rotatablymounted thereon, a work; supporting table, means supporting said tablein said frame for reciprocatory movement past said grinding wheel, acrusher holder, rotatable crushing means on said holder for truing thesurface of the grinding wheel, means carrying said holder on said tablefor movement in vertical .and horizontal directions relative theretocomprising a base portion fixed to said table, a support means carriedin said base portion for horizontal sliding movements relative thereto,means in said support means carrying said crusher holder for verticalsliding in said support means, power operated means operativelyconnected to said holder for moving said holder sequentially first inone of said directions at a controlled rate to cause approach of theaxes of the grinding wheel and the crushing means, and then in the otherdirection to gradually change the distance

